1. Field of the Invention
The present invention relates to a coated cutting tool (cemented carbide insert) useful for grooving or parting of steel components, such as bars or tubes, not only of stainless steels of different compositions and microstructures but also of non-stainless steels such as low carbon steels and low and medium alloyed steels.
2. Description of Related Art
In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
When machining low and medium alloyed steels and stainless steels with cemented carbide tools, the cutting edge is worn according to different wear mechanisms. Examples of such mechanisms include chemical wear, abrasive wear, adhesive wear and edge chipping. In bad cutting conditions problems with bulk and edge line breakages commonly occur. Furthermore, different cutting variables, such as cutting speed and cutting feed rate, and external conditions, such as dry or wet machining and heavy vibrations of the work piece, require a plurality of different properties of the cutting edge.
It has been very difficult to improve all of the plurality of preferred tool properties simultaneously. Therefore, commercial cemented carbide grades have been optimized with respect to one or only a few of these wear types and, hence, to specific application areas.
U.S. Pat. No. 6,062,776 discloses a coated cutting insert particularly useful for dry and wet machining in low and medium alloyed steels and stainless steels, with or without raw surface zones, under severe conditions such as vibration, long overhang, and recutting of chips. The insert is characterized by a WCxe2x80x94Co cemented carbide with a low content of cubic carbides, a rather low W-alloyed binder phase, and a coating including an innermost layer of TiCxNyOz with columnar grains and a top layer of TiN and an inner layer of xcexa-Al2O3.
Swedish patent application SE 9901149-6 discloses a coated cutting insert, particularly useful at high cutting speeds, for use on stainless steels of different compositions and microstructures. The insert is also useful for the milling of non-stainless steels such as low carbon steels and low and medium alloyed steels. The coated WCxe2x80x94Co based cemented carbide insert is characterized by a specific composition range of WC/Co without any addition of cubic carbides, a low W-alloyed Co binder, a narrowly defined range of average WC grainsizes, and a hard and wear resistant coating including a multilayered structure of sublayers of the composition (TixAl1-x)N with repeated variation of the Ti/Al ratio.
It has now surprisingly been found that a combination of a modified cemented carbide substrate described in the above mentioned U.S. Pat. No. 6,062,776 and the coating described in the above mentioned SE 9901149-6 results in excellent cutting performance in grooving or, in particular, parting of steel, including stainless steel.
A cutting tool insert, for parting of steel and stainless steel, and a method of making the same is provided. The cutting tool insert is comprised of a cemented carbide body and a coating wherein the cemented carbide body consists of WC with an average grain size of about 1.4 mm, 12-13 wt-% Co, 0.4-1.8 wt-% TaC+NbC, and a low W-alloyed binder phase with a CW-ratio of 0.82-0.91. The coating is comprised of a multiple layers. The first (innermost) layer is 0.1-0.5 xcexcm of TiN. A second layer is comprised of a multilayered structure of 0.05-0.2 xcexcm thick sublayers. The sublayers are of a composition (TixAl1-x)N in which x varies repeatedly between the two ranges 0.45 less than x less than 0.55 and 0.70 less than x less than 0.80. A first sublayer, adjacent to the TiN bonding layer, is of a composition (TixAl1-x)N having an x-value of 0.45 less than x less than 0.55. A second sublayer is of a composition (TixAl1-x)N having an x-value of 0.70 less than x less than 0.80 and a third sublayer is of a composition (TixAl1-x)N having x of 0.45 less than x less than 0.55. The sequence of sublayers alternates and repeats until 12-25 sublayers are built up. After the multilayered structure, a third layer of (TixAl1-x)N, where x is 0.45 less than x less than 0.55, is deposited to a thickness of 0.1-0.5 xcexcm. A fourth and outermost layer of TiN is deposited to a thickness of 0.1-0.2 xcexcm. The total coating thickness is 1-8 mm and the thickness of the second layer constitutes 75-95% of the total coating thickness.